Re: [PATCH 4/6 v7] ext4: Lock i_mutex for punch hole

[Andreas Dilger <adilger@dilger.ca>]

On 2011-08-31, at 12:49 PM, Allison Henderson wrote:
> On 08/30/2011 05:31 PM, Andreas Dilger wrote:
>> On 2011-08-30, at 6:28 PM, Allison Henderson wrote:
>>> This patch modifies the fallocate routine to lock i_mutex during
>>> the punch hole operation.
>>> 
>>> Yongqiang noticed that the vfs layer locks i_mutex for truncate,
>>> but not fallocate, so the fallocate routine will need to take
>>> care of locking i_mutex.  Otherwise a page may be mapped after
>>> punch hole has released the pages, but before i_data_sem is
>>> locked to release the blocks in the extent tree.
>> 
>> If the VFS is locking i_mutex for truncate, shouldn't the locking for
>> fallocate() also be done in the VFS?
> 
> Alrighty, I will do some poking around with this idea first.  I dont know if other files systems are already locking i_mutex during fallocate, and it may be the case that not all filesystems need i_mutex locked for fallocate.  So I'll do a little research first, but I will post back with what I find.  Thx!

Probably a good idea to bring up this issue on linux-fsdevel.

>>> Signed-off-by: Allison Henderson<achender@linux.vnet.ibm.com>
>>> ---
>>> :100644 100644 9124cd2... 007fb08... M	fs/ext4/extents.c
>>> fs/ext4/extents.c |   10 +++++++---
>>> 1 files changed, 7 insertions(+), 3 deletions(-)
>>> 
>>> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
>>> index 9124cd2..007fb08 100644
>>> --- a/fs/ext4/extents.c
>>> +++ b/fs/ext4/extents.c
>>> @@ -3774,8 +3774,13 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
>>> 	if (mode&  ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
>>> 		return -EOPNOTSUPP;
>>> 
>>> -	if (mode&  FALLOC_FL_PUNCH_HOLE)
>>> -		return ext4_punch_hole(file, offset, len);
>>> +	mutex_lock(&inode->i_mutex);
>>> +
>>> +	if (mode&  FALLOC_FL_PUNCH_HOLE) {
>>> +		ret = ext4_punch_hole(file, offset, len);
>>> +		mutex_unlock(&inode->i_mutex);
>>> +		return ret;	
>>> +	}
>>> 
>>> 	trace_ext4_fallocate_enter(inode, offset, len, mode);
>>> 	map.m_lblk = offset>>  blkbits;
>>> @@ -3789,7 +3794,6 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
>>> 	 * credits to insert 1 extent into extent tree
>>> 	 */
>>> 	credits = ext4_chunk_trans_blocks(inode, max_blocks);
>>> -	mutex_lock(&inode->i_mutex);
>>> 	ret = inode_newsize_ok(inode, (len + offset));
>>> 	if (ret) {
>>> 		mutex_unlock(&inode->i_mutex);
>>> --
>>> 1.7.1
>>> 
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>> 
>> 
>> Cheers, Andreas
>> 
>> 
>> 
>> 
>> 
> 


Cheers, Andreas